1. Field of the Invention
This invention relates to a method of manufacturing a radiation detector including a conversion layer for converting radiation into charges.
2. Description of the Related Art
Radiation detectors that image radiation are used in various fields including a medical field. Here, description will be given in detail of a construction of such a radiation detector. As illustrated in FIG. 11, a conventional radiation detector 60 includes a CdTe layer 51 for converting radiation into carriers of electron-hole pairs, a sensor substrate formed by charge blocking layers 52 and 57 laminated so as to cover both surfaces of the CdTe layer 51, and a glass active matrix substrate 54. A layer including CdTe layer 51, the charge blocking layers 52 and 57 is connected to the active matrix substrate 54 via conductive carbon bump electrodes formed on pixel electrodes of the active matrix substrate 54.
The CdTe layer 51 is a conversion layer that converts radiation into charges. The layer largely contributes to manufacturing the radiation detector 60 of high performance. This is because lower or non-uniform conversion efficiency of converting radiation into charges in the Cd Te layer 51 may cause a decreased detecting property of the radiation detector 60.
Regarding this state, various approaches of generating a CdTe layer 51 of higher performance than before have been developed. For instance, such a design is given as doping the CdTe layer 51 with chlorine to generate a high-performance CdTe layer 51. See, for example, Japanese Patent No. 4269653.
Specifically, such a CdTe layer is formed on a substrate by closed spaced sublimation. At this time, CdCl2 is mixed with a material or a chlorine-containing gas is introduced into the material in gaseous phase, whereby a chlorine-doped Cd Te layer is generated. Doping with chlorine allows enhanced performance of the radiation detector.
The CdTe layer generated in such a manner has minute assembled crystals, and is called a polycrystalline film. The method of generating the CdTe layer of the polycrystalline film is advantageous to manufacturing the radiation detector having a large area.
Moreover, the CdTe layer may be doped with zinc for increasing performance thereof. In this case, the CdTe layer is doped with chlorine and zinc.
The conventional configuration as above, however, has the following drawbacks.
That is, merely doping the Cd Te layer with chlorine as conventional leads to insufficiently enhanced performance of the CdTe layer.
That is, the conventional manufacturing method has a drawback that each section of the radiation detector fails to have a uniform detecting property. It has been known that an interface between the CdTe layer and the charge blocking layers manufactured by the conventional method contains a Zn-rich region appearing therein. The Zn-rich region appears in the interface as an uneven block, and causes a non-uniform electric conduction property and the like in the interface. Such the uneven interface may result in a non-uniform conversion property of radiation or a non-uniform collection property of carriers.
There also arises a drawback that the CdTe layer 51 is insufficiently changed into N-type. Originally, the CdTe layer 51 operates by heterojunction of the CdTe layer 51 and the charge blocking layer 52. That is, the CdTe layer 51 and the charge blocking layer 52 are preferably formed into like a diode. For that purpose, the CdTe layer 51 should be certainly an N-type semiconductor. On the other hand, since the conventional construction includes the CdTe layer 51 doped with chlorine, the CdTe layer 51 seems to be certainly changed into N-type.
However, in actual, the CdTe layer 51 is not changed into N-type sufficiently considering an amount of doped chlorine atoms. That is, the conventional construction of the radiation detector achieves insufficient semiconducting properties of the CdTe layer 51, leading to reduction in detectability of the radiation detector.